Replace wxST_MARKUP style with wxControl::SetLabelMarkup().

This is an incompatible change which removes the wxStaticText-specific
wxST_MARKUP style and adds wxControl::SetLabelMarkup() replacing it.

It doesn't actually change anything yet but it simplifies wxStaticText code a
lot by getting rid of many markup-related functions in it which had to behave
differently depending on whether wxST_MARKUP was used or not and also paves
way for adding markup support for the other controls in the future.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67055 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/stattext.h

@@ -56,6 +56,14 @@ protected:
 
     virtual wxString DoGetLabel() const;
     virtual void DoSetLabel(const wxString& str);
+    virtual bool DoSetLabelMarkup(const wxString& markup);
+
+private:
+    // Common part of SetLabel() and DoSetLabelMarkup().
+    typedef void (wxStaticText::*GTKLabelSetter)(GtkLabel *, const wxString&);
+
+    void GTKDoSetLabel(GTKLabelSetter setter, const wxString& label);
+
 
     DECLARE_DYNAMIC_CLASS(wxStaticText)
 };